1. Field of the Invention
The present invention relates generally to the manufacture of glass articles that are formed by press molding, and, more particularly, to methods and apparatus for providing increased productivity in a glass manufacturing process by utilizing cryogen that preferably is introduced through tube-in-a-tube type injectors, with a flow of cryogen from a high pressure source being fed through the inner of the injector tubes, and with cryogen from a low pressure source being continuously fed through the outer of the injector tubes to provide cooling and to keep the high pressure injector tubes purged of ambient air to prevent moisture condensation on and ice formation in and about the high pressure injector tubes.
2. Prior Art
In the molding of hollow glass articles such as beer mugs and the like using the "press-molding method," a gob of glass typically is inserted into a mold where it is pressed to form an article of desired form. Ambient air is used, not only to cool the newly formed glass article, but also to cool the press mechanism.
In the press molding of glass, it is customary to utilize flows of air as a cooling gas. Usually a gentle flow of air is established across the mold area, which is referred to by the term "low pressure air flow." Also, provision is made to direct a more intense, blast like flow of air toward and into the hollow interiors of newly molded articles while the articles are still contained within their mold cavities to speed cooling and solidification of the articles so that the articles can be removed as quickly as possible from their molds. The relatively high velocity flow of air that is employed intermittently (i.e., at times when a newly molded article is moved from the pressing station and is positioned in a cooling station so that the article is aligned with an injector tube through which a high velocity flow of air discharges) is referred to by the term "high pressure air flow."
In order to speed the cooling of molded glass articles to diminish their mold retention times, proposals have been made to indirectly cool the articles by providing at least portions of their molds with cooling passages through which a fluid coolant is circulated. However, the degree to which mold cooling can be used to indirectly cool molded glass articles is limited not only by the tendency of this approach to induce defects (the number of defects induced in molded glass articles increases as mold temperatures are diminished), but also by the cost of forming cooling passages in the molds, and by the cost of providing suitable apparatus for maintaining controlled flows of coolant through the cooling passages.
While mold cooling provides some assistance in diminishing mold retention times, the retention times during which newly molded glass articles must be held in their molds to effect proper solidification continue to form "bottlenecks" that obstruct efforts to increase the productivity of existing molding equipment.
3. The Referenced Parent Cases
As is explained in the referenced Parent Cases, the use of flows of cold cryogen vapor that are introduced into mold cavities is applicable to a variety of glass molding techniques including press molding and blow molding. A flow of cold cryogen can be introduced into a mold cavity to cool a newly molded article and to cool such apparatus as has been used in the forming of the article. Thus molds can be recycled and reused more quickly than has previously been thought to be possible, and a very significant increase in productivity of molded articles is achieved while utilizing existing production facilities.
While uneven cooling of a molded glass article may create stress points, it does not cause significant warpage. Such stress points as are created in the forming of molded glass articles typically are dealt with by passing the articles through a lehr, a long furnace which tempers the glass by reheating it to about 900 degrees Fahrenheit, whereafter the glass is gradually cooled to allow the stress points to relieve themselves. Since the molded glass articles are put through a lehr, the only cooling that is necessary in conjunction with the actual molding of glass is a sufficient amount of cooling to assure that newly molded articles will retain their shape once they are extracted from the molds that have been used to form the articles.
What the inventions of the Parent Cases recognize is that, in the molding of a hollow glass article, the only cooling of a newly molded glass article that is necessary in order to permit the immediate discharge of the article from its mold is an amount of cooling that is adequate to give the glass enough strength to hold its shape. The inventions of the referenced Parent Cases address this very minimal need for cooling in a special way, namely by employing a very fast acting cooling technique that results in creating what essentially amounts to a solidified "skin" on the interior surface of a newly formed hollow glass article. Once this interior "skin" has been formed and has cooled sufficiently to act as a stable mainstay that will render the newly molded article shape-stable, the mold can be opened and the newly molded article can be removed.
The fast formation of an adequately cooled and rigidified interior "skin" permits a newly molded glass article to be extracted far more quickly from its mold than previously has been possible with prior glass molding cooling techniques. Because the mold can be recycled and reused more quickly than has previously been thought to be possible, and a very significant increase in productivity of molded articles is achieved while utilizing existing production facilities.